Many shafts used as power transmission components for automobiles or the like are made of metal and are created by a cutting operation, so the product cost is high and the weight is heavy.
An injection molded shaft 100 made of synthetic resin in FIG. 10 was proposed to solve such problems. In the injection molded shaft 100 illustrated in FIG. 10, a gear 101 and an inward flange 102 are formed integrally with one end of a cylindrical shaft body 103 and a rotary torque is transferred to another rotary component (not illustrated) via the gear 101 (see JP-A-2003-33947).
However, since the twisting stiffness of the cylindrical shaft body 103 is large in the injection molded shaft 100 illustrated in FIG. 10, even when a rotary torque is applied impulsively, the shaft body 103 cannot undergo sufficient twisting deformation and the shock caused by sudden changes in torque could not be absorbed by twisting deformation of the shaft body 103. Therefore, in the injection molded shaft 100 illustrated in FIG. 10, rotation transmission components such as the gear 101 receive a shock caused by sudden changes in torque, possibly breaking rotation transmission components such as the gear 101.
Therefore, the invention provides an injection molded shaft that can absorb a shock caused by sudden changes in torque by undergoing twisting deformation of a shaft body when sudden changes in torque are applied.